A launch vehicle provides the velocity needed by a spacecraft to escape Earth's gravity and set it on its course for Mars.

Read more about the launch vehicle on these pages.

Rovers Launched on Delta IIs

When mission planners are considering different launch vehicles, what they take into consideration is how much mass each launch vehicle can lift into space. The Boeing Delta II launch vehicle was selected for the Mars Exploration Rover mission because it has the right liftoff capability for the weight requirements and because it's extremely reliable.

Deltas are expendable launch vehicles (ELVs), which means they are only used once.

The Rover A mission used a standard Delta II 7925 when it launched June 10, 2003. The later Rover B launch on July 7, 2003 needed more energy to get to Mars, so it launched on a Delta II 7925H, where "H" stands for "Heavy." Learn about the launch vehicle differences and the reasons for them.

The major elements of the Delta Rockets for the MER missions, however, are nearly identical. Each launch vehicle consists of:

Solid Rocket Motors: Used to increase engine thrust; 9 total, 6 of which are lit at liftoff, 3 a minute into flight

Payload Fairing:
Thin metal shroud or nose cone to protect the spacecraft during the ascent through Earth's atmosphere

Stage II: Fuel and oxidizer and the vehicle's "brains"; fires twice, once to insert the vehicle-spacecraft stack into low Earth orbit and then again to orient the third stage prior to it firing

Stage III: Solid rocket motor provides the majority of the velocity change needed to leave Earth orbit and inject the spacecraft on a trajectory to Mars; connected to the spacecraft until done firing, then separates